In some methods of generating an output DC voltage of a power supply unit for gas discharge processes, a first DC voltage is transformed into a second DC voltage of a predetermined voltage range in a first voltage transformation stage, and in a second voltage transformation stage the output DC voltage is generated from the second DC voltage. A method of this type and a corresponding device are disclosed, for example, in DE 196 27 497 A1.
Gas discharge processes have different impedances due to the most different requirements in the process and particularities of the system technology. This means that different discharge voltages must be provided to obtain the required specific power conversion. Moreover, the voltage required for striking a gas discharge process is often higher than that for maintaining the gas discharge process.
DE 196 27 497 A1 discloses a plasma generator with a strike enhancement circuit. The strike enhancement circuit generates a high voltage at a high impedance to initiate a plasma in a plasma or sputter chamber. The strike enhancement circuit has a plurality of diode bridges which act as full-wave rectifiers. The transformer secondary of the power supply is connected to the alternating current (AC) inputs of each diode bridge via isolation capacitors. The direct current (DC) connections of the diode bridges are connected in series and the added voltage is supplied to the plasma chamber via the input connections. Each diode bridge also comprises a storage capacitor which connects positive and negative DC connections. Positive and negative voltage peaks of the transformer secondary waveform are stored in the storage capacitors. A voltage is present at the DC outputs, which is large enough to initiate plasma discharge. If plasma is present, the impedance of the isolation capacitors prevents the strike circuit from supplying the high strike voltage. The conventional device and the associated method are typically not suited to control the DC voltage at the output of the plasma generator over a wide voltage range.